The major objective of the proposed work is to study the genetic properties and induced effects of a "mutator mechanism" discovered in this laboratory. Both the 2nd and 3rd chromosome of the "mutator" line, independently and jointly, have the capability of inducing lethal, viability and visible mutations. It has recently been discovered that the "mutator mechanism" induces a non-trivial rate of male recombination. During the coming year the nature of these properties will be investigated in greater detail. Theoretical studies of the impact of mutation on selection and inbreeding will be continued. Once the nature of the mutator mechanism is understood experiments requiring a high rate of spontaneous mutation will be initiated.